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-Wdiscarded-qualifiers warning in _ctypes_test.c my_strchr() under FORTIFY_SOURCE=3 #149707

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-Wdiscarded-qualifiers warning in _ctypes_test.c my_strchr() under FORTIFY_SOURCE=3#149707
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buildThe build process and cross-buildextension-modulesC modules in the Modules dirtestsTests in the Lib/test dirtopic-ctypestype-bugAn unexpected behavior, bug, or error

Description

@utkonos
utkonos
opened on May 12, 2026

Bug report

Bug description:

Building 3.14.5 with gcc 15.2 and --enable-slower-safety produces this warning:

    default: ./Modules/_ctypes/_ctypes_test.c: In function ‘my_strchr’:
    default: ./Modules/_ctypes/_ctypes_test.c:451:12: warning: return discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
    default:   451 |     return strchr(s, c);
    default:       |            ^~~~~~

Build environment: Ubuntu 26.04 LTS, gcc 15.2.0, configure with:

./configure --enable-optimizations --with-lto --enable-bolt --enable-safety --enable-slower-safety --with-system-expat CXX=/usr/bin/g++ CFLAGS="-flto=auto" LDFLAGS="-flto=auto"

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

Activity

  1. utkonos
    added
    type-bugAn unexpected behavior, bug, or error
    on May 12, 2026
  2. picnixz
    added
    testsTests in the Lib/test dir
    topic-ctypes
    extension-modulesC modules in the Modules dir
    buildThe build process and cross-build
    on May 12, 2026
  3. vstinner
    added a commit that references this issue on May 15, 2026

    gh-149707: Fix compiler warning in _ctypes_test on strchr() (#149791)

    5465b69

  4. vstinner commented on May 15, 2026

    @vstinner
    vstinner
    on May 15, 2026
    Member

    On Linux with the glibc, when using C23, strchr(text, ch) return type is const char* if text type is const char*.

    See for example the glibc commit which introduced C23 support in string/string.h.

    The string.h code is now:

    extern char *strchr (const char *__s, int __c)
     __THROW __attribute_pure__ __nonnull ((1));
# if __GLIBC_USE (ISOC23) && defined __glibc_const_generic && !defined _LIBC
#  define strchr(S, C)                                         \
  __glibc_const_generic (S, const char *, strchr (S, C))
# endif
  5. miss-islington
    added 2 commits that reference this issue on May 15, 2026

    pythongh-149707: Fix compiler warning in _ctypes_test on strchr() (py…

    78043d4

    pythongh-149707: Fix compiler warning in _ctypes_test on strchr() (py…

    00a3e42
  6. vstinner
    closed this as completedon May 15, 2026
  7. vstinner
    added 3 commits that reference this issue on May 15, 2026

    [3.13] gh-149707: Fix compiler warning in _ctypes_test on strchr() (#…

    782880b

    [3.14] gh-149707: Fix compiler warning in _ctypes_test on strchr() (#…

    98c036b

    [3.15] gh-149707: Fix compiler warning in _ctypes_test on strchr() (#…

    8d32ae7
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